Whisk together the all-purpose flour, milk, water, baking powder, and salt in a bowl until the mixture is smooth. This will ensure that all the ingredients are well combined.

Heat oil in a deep fryer or a large pot to a temperature of 365 degrees F (185 degrees C). The oil should be hot enough to fry the fish evenly and create a crispy texture.

Dip the fish fillets into the prepared batter, ensuring that each fillet is fully coated. This will ensure that every bite of the fish is covered in delicious batter.

Carefully lower the battered fish fillets into the hot oil, using tongs or a slotted spoon. Be cautious to prevent any oil splatters or burns.

Fry the fish fillets for about 2 minutes per side, or until they are cooked through and golden brown. This will give the fish a crispy exterior while keeping the inside tender and flavorful.

Once the fish is cooked, remove it from the oil using a slotted spoon and place it on paper towels to drain excess oil.